The progressive growth of antigen-expressing tumors despite the presence of tumor antigen-specific CD8+ T cells is a central problem in the field of anti-tumor immunity. Although one hypothetical mechanism of escape is T cell anergy, this process in the tumor setting is poorly defined. Using a TCP transgenic T cell model that allows recovery of sufficient numbers of T cells for analysis ex vivo, we have recently observed that tumors do induce antigen-specific hyporesponsiveness of anti-tumor CD8+ T cells and not of irrelevant T cells, consistent with a form of T cell anergy. We also have obtained preliminary data that tumor-induced T cell hyporesponsiveness does not occur when lymphopenia-induced homeostatic proliferation is permitted. Understanding the mechanism of the induction and reversal of T cell anergy should have great impact in our ability to maintain the functionality of tumor antigen-specific T cells in vivo, and enable the development of interventions that can be translated to the clinic. The first specific aim is to determine the mechanism of T cell-intrinsic hyporesponsiveness of TCR transgenic T cells in tumor bearing mice. TCR Tg T cells will be analyzed ex vivo for deficiencies in signal transduction events triggered by TCR/CD28 stimulation, and for molecular alterations using gene expression profiling. CAR Tg T cells and adenoviral vectors will be utilized to examine the causal relationship between observed changes and T cell dysfunction. The second specific aim is to explore and understand the mechanism by which T cell responsiveness is restored through homeostatic proliferation in vivo. Homeostatic signals will be delivered to anergic T cells by manipulating the host (transferring into RAG2-/- mice), manipulating the tumor (transfecting to express IL-7 and/or IL-15), or by manipulating the T cells (transduction with constitutively active Stat5). T cells will be analyzed for functional and biochemical properties, and alterations will be correlated with tumor rejection capability. The third specific aim is to apply knowledge of maintenance of T cell responsiveness out of this reductionist model toward rejection of established tumors in normal mice. T cell subsets from normal C57BL76 mice will be manipulated to affect homeostatic factors and tested for rejection of B16 melanoma transfected to express the model antigen SIY. T cell transduction and tumor transfectants will be examined using factors identified to be useful from the TCR Tg model and mechanisms of improved tumor control will be dissected.